AFP reports that this decision overturned a lower court's ruling in favour of two Christian doctors who refused fertility treatment to a lesbian and cited religious grounds.
The woman, Guadalupe Benitez, successfully filed suit against the doctors and their medical group in 2004 on the basis that their refusal to treat her violated California's anti-discrimination laws.
However an appeal court in San Diego ruled against Benitez, a decision that led to the supreme court ruling.
In an unanimous decision the justices ruled that Benitez was entitled to be treated like other patients with the same condition, and that constitutional protections for religious liberty do not excuse unlawful discrimination.
Benitez is quoted as saying, "It's wrong and shocking that some doctors felt their religious beliefs allowed them to ignore the law and discriminate. This isn't just a win for me personally and for other lesbian women. It's a win for everyone."
Earlier this year, the state's Supreme Court overturned a state ban on same-sex marriage in a landmark decision.